My strat (This lvled a sorc for me to lvl 65 in ~12 hrs total)

Lvls 1-5: Join a 8-player game and clear blood moor. You'll get here in moor itself.

Lvls 5-7: Do A1 quests including Den/Blood Raven/Cain.

Lvls 8-14: Clear Black Marsh and Tamoe in 8-player games.

Lvls 15-20: Clear Sewers in 8-player games.

Lvls 20-24: Arcane in 8-player games.

Lvl 25: Ancients

Lvls 26-50: Norm Baal Runs

Lvls 51-53: NM questing/rushing (NM Ancients)

Lvls 54-70: NM Baal Runs

Lvls 71-72: Hell Ancients and Hell Questing

Lvls 73+: Hell Baal Runs

Edit: @Mongo. 3 hours? I doubt that. I spent a WHILE lvling on norm baal runs, doing them at an average of 2:20/run.

400th post!